Existing DoD and municipal water supply systems typically lack considerations for counter-terrorism. The motives behind terrorist attacks on utility plants may be denial of service or human casualties. In this study, we focus on the latter, specifically on chemical and biological (CB) agent attacks on potable water systems. Due to the dilution effect, the areas upstream of the utility plant are not of much concern. The hazard associated with CB attacks downstream of the utility plant are currently not well understood and these form the focus of the proposed effort. The goal of this project is to develop an accurate fate and transport model and interface it with sensors and disinfectant feeders via the SCADA system to effectively monitor, detect, and neutralize CB agents introduced into water distribution systems. We selected an existing public domain hydraulics code called EPANET as the platform for the proposed effort. It is extensively used by the U.S. Army, the EPA and in the industry. During the proposed SBIR project, we will add necessary models and databases to EPANET and validate the model through tests in simulated water distribution loops. We will also interface the model with a representative SCADA system. The model can be used by military installations, the war fighter in the field or in foreign lands and by the water supply industry to monitor the water distribution networks for CB attacks and malfunctions in water treatment plants. In the event of an attack, the model can be used to predict the hazard zone and the rate of hazard spread, determine the location and strength of the agent source and devise appropriate countermeasures and emergency response procedures.